Boss RC-500 drift issue - no solution with current firmware

On Boss RC-500 if using playmode=Single for verse/chorus loops and you sync the two tracks with diferent lenghts to the internal rhythm (Loop.S=On), when it finishes playing the shorter one doesn't start from the beginning of longer one.
Made this video to ilustrate RC-500 drifting issue when using track1 loop.S=Off and track2 loops.S=On seetings because acording to • Video these are suposed to resolve it. When alternating between track 1 and 2 everything seems ok but, when I start to repeat just track 1, for me on the 4th repeat, the drift is evident. Any sugestions?
(I don't use the RC-500 default switch functions. Instead I programed switch1 to rec/ply track1, switch2 to rec/ply track2 and switch3 to stp/clr loop)